使用蒙特卡罗模拟和放射色胶片对超声兼容妇科高剂量率近距离治疗筒的声致透明材料进行剂量学研究。

Dosimetry of a sonolucent material for an ultrasound-compatible gynecologic high-dose-rate brachytherapy cylinder using Monte Carlo simulation and radiochromic film.

机构信息

Department of Physics and Astronomy, University of Calgary, Calgary, AB, Canada; Medical Physics Department, Tom Baker Cancer Centre, Calgary, AB, Canada.

Department of Physics and Astronomy, University of Calgary, Calgary, AB, Canada; Medical Physics Department, Tom Baker Cancer Centre, Calgary, AB, Canada; Department of Oncology, University of Calgary, Calgary, AB, Canada.

出版信息

Brachytherapy. 2021 Jan-Feb;20(1):265-271. doi: 10.1016/j.brachy.2020.08.024. Epub 2020 Oct 7.

DOI:10.1016/j.brachy.2020.08.024

PMID:33039331

Abstract

PURPOSE

he purpose of this study was to study the dosimetric characterization of sonolucent material "TPX" to be used toward gynecologic high-dose-rate brachytherapy treatments using ultrasound-compatible cylinders in non-model-based dose calculation workflows.

METHODS

Monte Carlo simulations were performed using EGSnrc application egs_brachy in cylinders of polymethylpentene (TPX) plastic, water, and PMMA. Simulations were performed of five 192Ir sources placed longitudinally in ∼3.7 cm diameter, 5.0 cm length cylinders (matching physical cylinders used in film measurements). TPX and PMMA dose distributions and percentage depth dose curves were compared relative to water. Film measurements were performed to validate egs_brachy simulations. TPX and PMMA cylinders were placed in a water tank using 3D-printed supports to position film radially and touching the surface of the cylinders. The same five 192Ir dwell positions were delivered as simulated in egs_brachy.

RESULTS

The egs_brachy and film percentage depth doses agreed within film uncertainties. The egs_brachy relative dose difference between TPX and water was (0.74 ± 0.09)% and between PMMA and water was (-0.79 ± 0.09)% over the dose scoring phantom. Dose differences for TPX and PMMA relative to water were less than ± 1% within 5 cm of the cylinder surface.

CONCLUSIONS

In a solid sonolucent sheath of TPX, the dosimetric differences are comparable with PMMA and other applicator materials in clinical use. No additional uncertainty to dose calculation is introduced when treating through TPX cylinders compared with current applicator materials, and therefore, it is acceptable to perform gynecologic brachytherapy treatments with a sonolucent sheath inserted during radiation delivery.

摘要

目的

本研究旨在研究声透明材料“TPX”的剂量学特性，以便在非模型化剂量计算工作流程中，使用超声兼容的圆柱体进行妇科高剂量率近距离放射治疗。

方法

使用 EGSnrc 应用程序 egs_brachy 在聚甲基戊烯（TPX）塑料、水和 PMMA 圆柱体中进行蒙特卡罗模拟。在直径约 3.7cm、长 5.0cm 的圆柱体（与用于胶片测量的物理圆柱体匹配）中，模拟了五个 192Ir 源的纵向放置。将 TPX 和 PMMA 的剂量分布和百分深度剂量曲线与水进行比较。进行胶片测量以验证 egs_brachy 模拟。使用 3D 打印的支架将 TPX 和 PMMA 圆柱体放置在水箱中，以将胶片径向定位并接触圆柱体的表面。在 egs_brachy 中模拟了相同的五个 192Ir 驻留位置。

结果

egs_brachy 和胶片百分深度剂量在胶片不确定度范围内一致。egs_brachy 中 TPX 和水之间的相对剂量差为（0.74±0.09）%，PMMA 和水之间的相对剂量差为（-0.79±0.09）%，在剂量评分体模上。在距圆柱体表面 5cm 以内，TPX 和 PMMA 相对于水的剂量差异小于±1%。